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Phosphorus in Swine. I. Influence of Dietary Calcium and Phosphorus Levels and Growth Rate on Feedlot Performance of Barrows, Gilts and Boars¹

Virginia Polytechnic Institute and State University, Blacksburg 24061

Abstract

Three trials, each involving 192 crossbred gilts and barrows (two trials) or boars (one trial), were conducted to evaluate the effects of dietary Ca and P, sex and growth rate from birth to 60 to 70 days of age on feedlot performance. The following dietary treatments, as a percentage of NRC recommendations for barrows and gilts, were used: (1) 100% Ca and P, (2) 125% Ca and P, (3) 100% Ca and 125% P and (4) 100% Ca and 75% P. Pigs were fed an 18, 16 and 14% protein sequence. Final weight was 107 kilograms. Two additional trials, each involving 72 barrows and gilts with an average initial weight of 36 kg, were conducted to evaluate diets containing 100, 125 and 150% Ca and P. Daily gain and feed efficiency were depressed for barrows, gilts and boars fed the diet containing 100% Ca and 75% P. In a majority of the trials, barrows and gilts did not respond to Ca and P levels above NRC suggestions. However, the sex x diet interaction was significant for daily gain in trial 1; barrows fed the various diets had similar daily gains, whereas gilts fed 125% Ca and P had the highest gain. In the boar and gilt trial, there was a small but significant increase in daily gain during the growing phase when 125% Ca and P levels were fed. The nonsignificant sex x diet interaction indicated that gilts and boars responded similarly. There were no improvements in feed efficiency and daily feed intake. Generally, barrows and boars ate more and grew faster than gilts, but only boars were more efficient than gilts. Growth rate from birth to 60 to 70 days of age did not consistently influence the subsequent performance of barrows, boars or gilts. These results (1) show that feedlot performance of barrows, boars and gilts was reduced when less than the NRC-suggested level of P was fed; (2) lend support to the concept that boars require more than NRC-suggested levels of Ca and P to obtain maximum feedlot performance, and (3) suggest that gilts have a higher Ca and P requirement for maximum growth than do barrows.

¹ Appreciation is expressed to Charlie Babb, Carl Eure and K. L. Bryant for feeding and caring for the pigs; to Helen Bartlett for analytical workj to Cindy Atkins for typing the manuscript; to Dr. K. H. Hinkelman and Bill Woodall for statistical analysis, and to Smith-Douglass, Division of Borden Chemical, Borden, Inc., for partial financial support.

² Tidewater Research and Continuing Education Center.

³ Dept. of Anim. Sci.

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